Imaging Needs:

Imaging System:

Imaging cellular events in real time

Find out how Fang Huang, Jeorg Bewersdorf and colleagues achieve nanometer resolution at video frame rates using the sCMOS technology in the ORCA-Flash4.0 camera. Read now.

THE QUESTION

What are the genetic origins and functional importance of supernumerary B chromosomes?

In addition to the standard set of A chromosomes, in most eukaryotic species some individuals also carry one or more supernumerary B chromosomes (Bs). Considered unnecessary to normal growth and survival, Bs have been associated with phenotypic effects such as fitness and feritlity. Their modest effects suggest that Bs lack major functional genes, and researchers have associated them with only a few protein encoding genes so far.

THE BARRIERS

Recently, the sequencing of Bs in rye (Secale cereale)1 opened the opportunity for more detailed study. Comparison of As and Bs revealed numerous gene-derived sequences in the Bs, many traceable to origins as fragments of As. However, Bs’ origins and effects on the transcriptome remained largely unexplored.

Banaei-Moghaddam, et al,2 examined the sequences, chromosomal locations, and transcriptional activity of 15 gene-like B fragments from multiple subspecies of S. cereale. Ten of the 15 fragment sequences appeared in rye lacking B chromosomes, suggesting the presence of A counterparts. Fluorescence in situ hybridization using a Hamamastu ORCA-ER CCD camera and anti-sense probe derived from one such A counterpart confirmed the appearance of the fragment in both B and A chromosomes.

All 15 B fragments studied showed transcriptional activity, which varied by tissue type and rye species, as well as influences on the activity of A-located genes. The results demonstrate that Bs in rye contribute to the transcriptome. The authors propose a model for B evolution from A chromosomal origins.